This invention relates to actuators for controlling the operation of valves and especially for valves used in sprinkler systems for fire protection.
Automatic sprinkler systems for fire protection of structures such as office buildings, warehouses, hotels, schools and the like are required when there is a significant amount of combustible matter present. The combustible matter may be found in the materials from which the building itself is constructed, as well as in the building contents, such as furnishings or stored goods.
Of the various types of automatic sprinkler systems available, the preaction systems find widespread use. Preaction systems use an actuator which responds to a combination of signals from different detectors to trip a valve which provides water to the sprinkler piping network. Similar to the so-called xe2x80x9cdry-pipexe2x80x9d systems, the piping network in the preaction system is normally filled with air or nitrogen (and not water) prior to actuation. The preaction system can thus be used in unheated environments which are subject to below freezing temperatures without fear of pipes bursting due to water within the pipes expanding upon freezing.
When sufficiently pressurized, the behavior of the gas within the piping network may be used to indicate a fire condition and trigger actuation of the preaction system. Heat from the fire will cause sprinkler heads to open, allowing pressurized gas to escape from the piping network and resulting in a pressure drop within the system. Actuation of the system may be effectively triggered by this pressure drop.
Specifically, double interlock preaction systems are further advantageous because an alarm may be sounded to provide a warning before the sprinklers operate. Furthermore, failure, breakage or accidental opening of the sprinklers or a pipe in the piping network will not result in an unintentional discharge of water, since there is no water in the network until the system is actuated. Actuation for double interlock preaction systems requires that two or more separate signals be sensed.
Preaction systems are not without their disadvantages however. Traditional preaction systems, described above, which are triggered by a drop in air pressure within the piping network as the result of a sprinkler head opening in response to heat (along with a confirming signal from another sensor) usually maintain the sprinkler piping network at a relatively high internal pressure, typically on the order of 20% of the maximum water pressure in the system. The air pressure in such systems is used to control the release of the water to the piping network, and the valves typically operate at a mechanical advantage of about 1 to 5 air pressure to water pressure. The use of relatively high-air pressures becomes a problem with larger systems which tend to have a relatively large volume of air within the piping network. Higher air pressures and volumes require more powerful compressors, having higher capital and operating costs. Furthermore, the higher pressures mean that more air must be forced out of the piping network upon activation. The air in the network inhibits the free flow of water and, thus, increases the reaction time of the system. More air in the piping network also means that more moisture will be present, accelerating corrosion of the pipes.
There is clearly a need for a preaction sprinkler system having the ability to operate at relatively low system air pressures for providing a signal which activates the sprinkler system.
The invention concerns a purely pneumatic actuator for actuating a fire sprinkler system. The system is actuated when the actuator depressurizes a piston holding a valve controlling the flow of water to the sprinkler system closed. The actuator behaves like an AND gate in a logic circuit in that it will depressurize the piston and release the valve only when two separate pressure drops are manifest in the actuator. The actuator is thus connected to two separate sources of compressed air, one being the piping network of the sprinkler system, the other being a pilot line substantially co-located with the piping network. During a fire, heat-sensitive sprinkler heads on both networks open and release pressurized air within each network to the ambient. This causes pressure drops to occur in both networks which is sensed by the actuator. In response to the pressure drops, the actuator depressurizes the piston which allows the valve to open and supply water to the piping network for release through the open sprinkler heads onto the fire.
In the preferred embodiment, the actuator has a first chamber with a flexible first diaphragm mounted therein. The first diaphragm sealingly divides the first chamber into first and second chamber portions, both the chamber portions being in fluid communication with the cylinder. The second chamber portion has an opening providing fluid communication with the ambient, the opening being surrounded by a seat facing the first diaphragm. The first diaphragm is deflectable into sealing engagement with the seat to seal the opening when the cylinder is charged with a fluid, such as water from a pressurized source.
A second chamber having a flexible second diaphragm mounted therein which sealingly divides the second chamber into third and fourth chamber portions is preferably positioned above the first chamber. The third chamber portion is in fluid communication with a source of compressed air, for example, the pilot line network, and the fourth chamber portion is in fluid communication with the ambient. The fourth chamber portion has an aperture providing fluid communication with the first chamber portion, the aperture being surrounded by a second seat facing the second diaphragm. The second diaphragm is deflectable into sealing engagement with the second seat to seal the aperture when the third chamber portion is charged with compressed air from the pilot line network.
A third chamber having a flexible third diaphragm mounted therein and sealingly dividing the third chamber into fifth and sixth chamber portions is preferably positioned above the second chamber. The fifth chamber portion is in fluid communication with a second source of compressed fluid, for example, the piping network. An elongated plunger having one end positioned within the sixth chamber portion and engagable with the third diaphragm, and the other end positioned within the third chamber portion and engagable with the second diaphragm is slidably movable between the sixth and third chamber portions. The third diaphragm is deflectable into engagement with the one end of the plunger when the fifth chamber portion is charged with compressed air form the piping network, and the plunger is thereupon forced into engagement with the second diaphragm, thereby forcing the second diaphragm into sealing engagement with the second seat. The second diaphragm will be deflected out of engagement with the second seat only when both the fifth and the third chamber portions are vented to a lower pressure, as when sprinkler heads on both the pilot line network and the piping line network are open concurrently and vent the compressed air from these networks to the ambient. As a result, fluid pressure in each the third and fifth chamber portions falls to a predetermined value which allows fluid in the first chamber portion to enter the fourth chamber portion and exit to the ambient. This allows the first diaphragm to deflect out of engagement with the first seat and allows water to flow from the cylinder through the second chamber portion and exit to the ambient, thereby depressurizing the piston and allowing it to move within the cylinder and release the valve which moves to the open position and supplies water to the piping network.
The invention also includes a reset valve for manually resetting the sprinkler system and preventing unintentional resetting during a fire. The reset valve has a valve body and a conduit extending through the valve body. One end of the conduit is in fluid communication with the third chamber portions and the other end is vented to the ambient. A valve seat is positioned in the one end of the conduit and a valve closing member is movably mounted within the conduit adjacent to the seat. The valve closing member is movable into sealing engagement with the seat to close the reset valve. The reset valve also has means for biasing the valve closing member out of engagement with the seat when fluid pressure within the one end of the conduit falls below a predetermined value. The biasing means thereby opens the reset valve and vents the third chamber portion to the ambient. Preferably, there is an identical reset valve in fluid communication with the fifth chamber portion as well. The reset valves prevent spurious pressure surges from pressurizing either of the third or fifth chamber portions and thereby accidentally resetting the system and, thus, cutting off the water supply during a fire.